Because on a contracted out NI code Isummer you would have paid less national insurance than you would had you paid under a contracted in NI code.
The difference you would have paid into your company pension. Your employer would have made the sure the correct amounts were being paid as NI or into your pension scheme.
So many people don't understand the contracted out system. I dont think it is in operation anymore.
Is democracy being by-passed in favour of the billionaires?
It was 2020 though, so perhaps things are different now.